Determination of vapor coating rate by x-rays emitted from said vapor



March 12, 1968 F. F. CILYO DETERMINATION OF VAPOR COATING RATE BY X-RAYS EMITTED FROM SAID VAPOR MEASURING 8 CONTROL EQUIPMENT Filed Jan. 6, 1965 MEASURING a CONTROL EQUIPMENT m MP W W W A m United States Patent 3,373,278 DETERMINATION OF VAPOR COATING RATE BY X-RAYS EMZTTED FROM SAID VAPOR Frank F. Ciiyo, Hinsdale, IlL, assignor to United States Steel Corporation, a corporation of Delaware Filed Jan. 6, 1965, Ser. No. 423,764 7 Claims. (Cl. 250-495) ABSTRACT OF THE DISCLOSURE Method and apparatus are provided for determining coating thickness in vapor deposition processes. Vapor density may be correlated with deposition rate, which in turn determines coating thickness at a given speed of travel of the substrate. The vapor density is determined by X-ray measurement. The energy source for the X-rays may be independent of the energy source for evaporation of coating material. However, if the latter energy source is adapted to generate the required X-rays, it may perform the dual function of evaporation and X-ray production.

This invention relates to vapor deposition of coatings, generally in vacuum, and is particularly concerned with apparatus and method for measurement of the vapor density of the coating material, prior to deposition, for use in control of coating thickness. The invention is especially advantageous in a continuous process, such as the coating of strip material which continuously moves through the vapor-deposition zone.

While of broader application, the invention is particularly applicable to thickness control in the vacuum-coating of steel strip with aluminum.

Also, as will appear hereinafter, the invention assumes its simplest form when employed in conjunction with apparatus wherein the coating vapor is evaporated from its source by a high-energy beam, such as that from an electron gun, which beam is capable of generating characteristic X-rays when it contacts evolved Vapor.

A measurement of the molecular vapor density of the material being deposited may be correlated with the deposition rate, and resulting coating thickness. Accordingly, a purpose of the invention is to provide means and procedures for the ready determination of the vapordensity measurements required, taking into account online problems in industrial coating installations, in order to provide a basis for process control of the factors affooting coating thickness. The latter may include, for eX- ample strip speed and rate of evaporation of coating component.

The vapor-density measurement of the invention is based on the principie that characteristic X-rays are produced when atoms of matter are bombarded by energetic particles, such as an electron beam, or other forms of energy. The Wave length of the characteristic X-rays depends primariiy on the atomic structure of the material being bombarded. The elements with low atomic weights are characterized by long Wave lengths that can be produced with low-energy beams; however, high-energy beams are necessary to produce the short wave lengths that characterize the elements with higher atomic numbers. The intensity of the characteristic X-rays depends primarily upon the number of atoms that the energy beam intercepts, the atomic number of the material, and the energy of the incident beam. If the cross-sectional area of the beam, its energy, and intensity are maintained constant, than the intensity of the characteristic X-rays will depend only on the density of the vapor emitted from the coating-material source. Since in vapor-deposition applications, an increased rate of evaporation of material from 3,373,278 Patented Mar. 12, 1968 the coating source results in increased vapor density, a measurement of this density constitutes a measurement of the evaporation rate, and the correlative rate and thickness of coating deposition, under given conditions.

The invention will be further described in conjunction with the drawing, wherein:

FIGURE 1 schematically depicts a typical vacuumcoating operation incorporating applicants invention, and

FIGURE 2 illustrates a modification of applicants invention suitable for use with the deposition arrangement of FIGURE 1, as well as in other situations where a separate source of energy beam may be advantageous.

With further reference to FIGURE 1, an electron gun 1 generates an electron beam 2 that is bent by a magnetic field, not shown, in a semi-circular pattern to heat and melt the evaporant 3 in crucible 4. Portions of the resulting coating vapor 5 will flow toward strip 6, under thermal influence, where they deposit to form the desired coating.

The electron beam 2 contacts the atoms of the coating vapor, as at points,7, with resulting production of the aforementioned characteristic X-rays 8. The X-ray detector 9 picks up a portion of these X-rays, which enter through aperture 9a provided with collimator slits.

The X-ray detector may take many forms, although it preferably should be capable of operation in high vacuum. The output of the detector is fed to conventional measuring and control equipment, adapted to amplify the detector output, eliminate scattered rays, and count the characteristic rays from the coating material. This equipment, including the detector, may be that shown in Norelco X-ray Instrument Brouchure, RC-212B 5M1 159 published by the Philips Electronics and Pharmaceuticals Industries Corporation of Mount Vernon, NY. Detector 9, for example, may be of the type incorporated in the universal X-ray spectrograph 52360, which is provided with collimator slits.

The coating operation is conducted in a vacuum, apparatus for production of which is conventional, and not shown. The achievement of the bent electron beam, as shown and described, may be by various methods, and details of one mode thereof maybe obtained, for example, from Patent No. 3,046,936 of John C. Simons, In, dated July 31, 1962.

In instances where a separate electron beam may be necessary for X-ray production, for vapor-density measuring purposes, the modification shown in FIGURE 2 is applicable, wherein an electron gun I is positioned in housing 10 which has apertures 10a for passage of an electron beam therethrough to anode 1a. Housing It) also has aperture 10b, which is oriented with its axis of flow opening generally parallel to the flow path of coating vapor, to permit passage of sample portions of coating vapor 5 therethrough, on its way from the vapor source, not shown, to the base material to be coated, not shown. The device is arranged to permit contact of electron beam 2 with the coating vapor, as at points 7, with resulting production of characteristic X-rays 8, a portion of which enter detector 9 through collimator 9a. The detector and related measurement and control equipment may be that described in conjunction with FIGURE 1.

While several embodiments of applicants invention have been shown and described, modifications within the spirit of the invention, such as will be apparent to those skilled in the art to which the invention pertains, may be made without departure from its scope as set forth in the following claims.

I claim:

1. Apparatus for vapor deposition of coatings on a substrate moving at a known speed comprising (a) means for forming a coating vapor;

(b) means for causing emission of X-rays from the coating vapor; and

9 a (c) means operable by said X-rays for determining vapor density; whereby coating thickness may be determined by correlation of the density of the coating vapor and substrate speed.

2. In a vapor-coating apparatus, means for measurement of density of coating vapor to permit coatingthickness determination, said means comprising a highenergy beam of electrons and the like, adapted to'contact coating vapor and produce characteristic X-rays upon such contact, and means for measuring a predetermined sampling of said X-rays, which said high-energy beam is adapted to evaporate the coating material to form coating vapor.

3. The apparatus of claim 2 in which the path of the high-energy beam is arcuate.

4. In a vapor-coating apparatus, means for measurement of density of coating vapor to permit coating-thickness determination, said means comprising a high-energy beam of electrons and the like, adapted to contact coating vapor and produce characteristic X-rays upon such contact, and means for measuring a predetermined sampling of said X-rays, said means further comprising a housing having an aperture adapted to permit passage of sample portions of coating vapor therethrough on its way from the vapor source to the material to be coated, said aperture being oriented with its axis of flow generally parallel to the flow path of said coating vapor, said housing being provided with means adapted to permit said high-energy beam to pass transversely of said coating-vapor aperture and means for said sample X-rays to enter said measuring means.

5. A method for vapor deposition of coatings comprising (a) providing a coating vapor;

(b) providing a substrate, moving at known speed, to

receive said coating;

(c) contacting the vapor with a high energy electron beam to produce X-rays; and determining coating vapor density by use of said X-rays; whereby coating thickness may be determined by correlation of the density of the coating vapor and substrate speed.

6. The method of measurement of density of coating vapor in a vapor-coating apparatus, to permit coatingthickness determination, said method comprising contacting said vapor with a high-energy beam of electrons and the like, adapted to produce characteristic X-rays upon such contact, and measuring a predetermined sampling of said X-rays to determine coating-vapor density, which said high-energy beam evaporates the coating material to form coating vapor.

7. The method of claim 6 in which the path of the high-energy beam is arcuate.

References Cited UNITED STATES PATENTS 3,230,110 1/1966 Smith 118-49.1 3,246,146 4/1966 Cohen et a1 250-495 ARCHIE R. BORCHELT, Primary Examiner.

RALPH G. NILS'ON, Examiner.

A. L. BIRCH, Assistant Examiner. 

